Many sewer lines, water lines, and other conduits in use today are in need of renovation. In many cases, this is due to the age of the conduits, being that the materials, such as brick and mortar, tend to deteriorate over time; for example, the walls of sewer lines are often subject to erosion due to the corrosive nature of sewer gases. Also, in some cases the wall of the conduit may have suffered structural failure or have been washed out.
A method for renovating these conduits which has generally met with great success is referred to in the industry as "sliplining." This involves inserting or "jacking" a liner pipe into the bore of the conduit so as to provide a renewed, smooth-walled passage for containing and enhancing the fluid flow. Typically, the liner pipe is formed of a semi-rigid yet resiliently flexible material, such as fiberglass, high-density polyethylene (HDPE), or polyvinyl chloride (PVC) for example. To complete the installation, a cement grout is usually injected into the cavity between the liner pipe and the old conduit.
However, while sliplining has met with considerable success in general, this application has ordinarily been limited to the renovation of conduits which are cylindrical in cross-section. In particular, it has heretofore proven virtually impossible to satisfactorily adapt this technique to the renovation of semi-elliptical conduits, such as are often encountered in older (e.g., 19th century) installations. As can be seen in FIG. 1A, a typical semi-elliptical conduit 10 comprises a tubular bore 12, formed by (a) an upper arch portion 14 which is generally semi-circular in cross-section, (b) somewhat flattened or vertical sidewall portions 16a, 16b, and (c) a generally horizontal floor portion 18, which is often dished or bowed downwardly at the center so as to form "channel" for the fluid. The semi-elliptical conduit thus resembles an inverted "U" in cross-section.
As was noted above, conduits of this type are often found in older installations, such as water and sewer lines in older metropolitan areas, and they are typically constructed of brick or other masonry. As a result, due to both age and the nature of their construction, these conduits are very frequently in need of repair. Unfortunately, conventional sliplining techniques have not proven to be a satisfactory solution.
FIG. 1B illustrates the nature of this problem. In particular, this shows that the shape of a traditional, circular cross-section slipliner 20 is poorly matched to the characteristic inverted "U" shape of a semi-elliptical conduit. This results in large gaps between the two, typically in the corner areas 24 where the floor and sidewalls of the conduit meet, and also along the top 26 of the conduit, where the circular liner pipe typically has a significantly smaller radius than that the of the masonry arch.
This lack of fit leads to several serious problems. Most seriously, the mismatch means that the bore 22 of the liner must be significantly smaller in cross-section than the that of the original semi-elliptical conduit. This means that the capacity of the renovated conduit would be much less than it was to begin with, in some cases down to 50% or less; this reduction of capacity is simply unacceptable in most systems, which are often already strained to their limits. Also, because of the gaps between the liner and the conduit, an excessively large quantity of grout will be required to fill the annular cavity.
Although it is thus apparent that cylindrical liner pipes are not satisfactory for sliplining semi-elliptical conduits, no economical alternative has heretofore existed. In short, owing to the way in which liner pipes are ordinarily manufactured, it is only economical to produce a circular (i.e., cylindrical) shape. For example, a material which is commonly used in sliplining work is Hobas.TM. fiberglass pipe, available from Hobas USA, Inc., Austin, Tex.; this material is formed by centrifugal casting inside a rotating mold, so that a circular cross-section is the only practical shape. The methods used in the manufacture of PVC and HDPE pipe typically rely on some form of rotary molding as well, and are thus similarly limited to producing a cylindrical shape. Moreover, because the great majority of sliplining jobs call for conventional cylindrical liner pipe, it is simply not economical for pipe manufacturers to make fundamental changes in their production methods in order to fill the relatively limited (although still significant) semi-elliptical conduit market; also, the dimensions and shapes of existing semi-elliptical conduits vary so greatly that it would be difficult or impossible for a manufacturer to provide a series of pipes specifically shaped to correspond to each of these installations.
As a result, the only alternative which has generally been available for renovating semi-elliptical conduits has been a technique which involves in-situ formation of the liner by a chemical process; however, this particular process is excessively expensive and fluid flow through the conduit must be interrupted for the duration of the work, which is usually difficult or impossible to do.
Accordingly, a need exists for an economical technique for allowing conventional liner pipe material to be used in the sliplining renovation of semi-elliptical conduits. Moreover, there is a need for such a technique which does not require excessive investment by a manufacturer in tooling for production of liners which are specially configured to match the shape of such conduits.